Every ecosystem on Earth is, to some extent, affected by human activities (Vitousek et al. Reference Vitousek, Mooney, Lubchenco and Melillo1997). Here, by summarizing the rationale and logical framework of environmental impact assessments, we discuss how their interpretation can be influenced by the perceived loss of ‘naturalness’. Specifically, we argue that: (1) the degree of naturalness of an area affected by a given human perturbation should not play any role in the assessment of the impact and (2) any change not evaluated against a specific social, economic or ethical background before the onset of the perturbation should be, in the first instance, characterized as negative.
Understanding the causes of changes at global scales poses major challenges due to the difficulties of identifying appropriate reference conditions. Because of the lack of reliable historical records, (i.e. the shifting baseline syndrome; Pauly Reference Pauly1995; Dayton et al. Reference Dayton, Tegner, Edwards and Riser1998), determining how pristine systems may have looked is usually difficult, so that our perception of past reference conditions is often vague or subjective. The use of anecdotal information or the reconstruction of historical conditions through the establishment of large-scale protection schemes have been indicated as potential options to define pristine reference conditions (Pauly Reference Pauly1995; Jackson Reference Jackson2001). Such knowledge has been suggested to be a valid tool to reset goals and expectations for alternative options of management of living resources and rehabilitation of degraded environments (for example fisheries and marine protected areas). Environmental scientists are, however, often confronted with human perturbations occurring at local or regional scales, where reference conditions can often be identified without the need to invoke historical or anecdotal scenarios and, importantly, their degree of naturalness is irrelevant to the practice of impact assessment. Furthermore, it is worth stressing that the reconstruction of historical scenarios generally consists of a snapshot of past conditions (here referred to as those prevailing in the area decades or centuries before the intervention of the disturbance under investigation) and therefore does not provide information on temporal and spatial scales of variation in the structure of assemblages of organisms, knowledge that is necessary for impact assessment or restoration practice.
Decision-making with respect to human impacts can be viewed as a three-step process. First, there is the identification of a real or perceived impact. Second is the quantification of impacts by environmental scientists (i.e. assessment) and, finally, there is interpretation and planning with regard to social and economic outcomes by managers and stakeholders.
Studies of environmental impact are generally concerned with the effects of disturbance or contamination over some defined scale, which is assessed by comparing the disturbed site with one or more reference sites unaffected by the specific intervention under investigation. Reference sites can be thought of as a random sample from a population of sites as in design-based approaches (Underwood Reference Underwood1992), or as a set of covariates correlated with the disturbed site as in model-based analyses (Stewart-Oaten & Bence Reference Stewart-Oaten and Bence2001). Irrespective of the approach used, reference sites are selected from the same geographical area as the disturbed site and are supposedly exposed to the same mean environmental conditions (for example climate, seasonality and history). In this context, the general quality of the environment has no role in the assessment of the impact. Independently of perceptions of good or bad background conditions, it is the relationship between descriptors of assemblages at disturbed and reference sites that provides the evidence from which to make inferences about ecological impacts. It is only in relative terms that the magnitude, direction and severity of ecological responses to human disturbances can be scrutinized scientifically. Reference to unobserved unquantified past conditions is unnecessary and irrelevant for the assessment of alterations owing to specific human interventions.
Once detected and quantified, ecological impacts are interpreted with respect to a complex array of social and economic considerations. It is only at this stage that attributes of the system threatened, such as richness of species/habitats or proportion of rare or endangered species/habitats must be taken into account to assess the relevance of the environmental alterations, which will obviously vary from one system to another. The interpretation of changes is, therefore, not absolute, but contingent on the type of habitat and organisms under threat. For example, alterations viewed as reasonably negligible in a degraded urban area could be interpreted as severe in a National Park. This does not, by any means, imply that the consequences of human perturbations are not negative and not worth minimizing when alternative options are available. Unplanned ecological changes should be, by default, considered as negative, ensuring that there is consideration of the intrinsic negative consequences of unpredicted changes in ecological structure or function caused by human activities. This approach would contribute to the conservation of what is left of relatively undamaged habitats, because it implies that a case for tolerating some impact is actually made and justified. The actual occurrence or consequences of impacts may, however, be judged to be irrelevant or unacceptable for some specific background environmental conditions or affected social and economic conditions.
For example, Brown and Sax (Reference Brown and Sax2004) argued that the current concern for biological invasions is only partially justified, because comparable, or of even greater magnitude, extinctions and migrations of species have occurred in the past without human intervention. As a consequence, determining whether a particular current change in some recipient environment as a result of biological invasions is harmful remains a subjective, rather than an objective scientific endeavour. It could vary from positive to negative according to the prevalent economic and social activities taking place in the area and to the ecological awareness of the individuals affected by any environmental changes (Brown & Sax Reference Brown and Sax2004).
The same principle should be embraced even when unpredicted increases in numbers of species are produced as side-effects of human perturbations. An increase in the number of species has no intrinsic positive value. Some habitats have fewer species or are less productive than others, but this does not imply that they are not worth conserving. Conservation biologists must carefully avoid the pitfall of always defining increases in numbers of species as positive changes (Angermeier Reference Angermeier1994). Any increase in numbers and types of species may put more pressure on the resources needed by the native species. For example, if we generally consider more species to be a good thing, we would endorse attempts to replace arid lands or deserts with forests. Other attributes of natural assemblages, such as composition, frequency of occurrence and relative abundances of species, must obviously be considered when assessing impacts owing to humans.
A very different situation is that where human interventions pursue a well-defined goal that has been established a priori, as in restoration or rehabilitation. In such cases, the decision-making process is reversed in comparison to the evaluation of impacts and knowledge of past reference conditions can be required to set realistic goals and expectations. In this case, planning the specific changes as a consequence of ecological, social or economic needs then precedes the work of those scientists who have responsibility to achieve the defined goals. Here, the predicted changes, including increases in species diversity, are obviously given an intrinsic positive value. The same careful consideration should nevertheless be given to the consequences of restoration as to issues arising from impacts. For example, is restoration of urban wetlands which results in increased numbers of arthropod vectors of human diseases inevitably desirable?
In conclusion, unplanned alterations to natural systems, when detected relative to reference background conditions, either pristine or degraded, should always be considered a priori to be negative. This is so whether or not they are identified as increases or decreases in ecological variables (including the number of species in an area). Whether or not to tolerate or manage an increase (or, for that matter, a decrease) requires demonstration that the outcome will be predicted to be positive in the light of economic or social criteria, as suggested by Brown and Sax (Reference Brown and Sax2004). Unless changes caused by human activities are properly evaluated to be positive, they should be minimized as a continuing priority to aid conservation. Within this context, knowledge of past natural conditions can be crucial for rehabilitation and restoration practice, but irrelevant for the interpretation of human impacts.
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Every ecosystem on Earth is, to some extent, affected by human activities (Vitousek et al. Reference Vitousek, Mooney, Lubchenco and Melillo1997). Here, by summarizing the rationale and logical framework of environmental impact assessments, we discuss how their interpretation can be influenced by the perceived loss of ‘naturalness’. Specifically, we argue that: (1) the degree of naturalness of an area affected by a given human perturbation should not play any role in the assessment of the impact and (2) any change not evaluated against a specific social, economic or ethical background before the onset of the perturbation should be, in the first instance, characterized as negative.
Understanding the causes of changes at global scales poses major challenges due to the difficulties of identifying appropriate reference conditions. Because of the lack of reliable historical records, (i.e. the shifting baseline syndrome; Pauly Reference Pauly1995; Dayton et al. Reference Dayton, Tegner, Edwards and Riser1998), determining how pristine systems may have looked is usually difficult, so that our perception of past reference conditions is often vague or subjective. The use of anecdotal information or the reconstruction of historical conditions through the establishment of large-scale protection schemes have been indicated as potential options to define pristine reference conditions (Pauly Reference Pauly1995; Jackson Reference Jackson2001). Such knowledge has been suggested to be a valid tool to reset goals and expectations for alternative options of management of living resources and rehabilitation of degraded environments (for example fisheries and marine protected areas). Environmental scientists are, however, often confronted with human perturbations occurring at local or regional scales, where reference conditions can often be identified without the need to invoke historical or anecdotal scenarios and, importantly, their degree of naturalness is irrelevant to the practice of impact assessment. Furthermore, it is worth stressing that the reconstruction of historical scenarios generally consists of a snapshot of past conditions (here referred to as those prevailing in the area decades or centuries before the intervention of the disturbance under investigation) and therefore does not provide information on temporal and spatial scales of variation in the structure of assemblages of organisms, knowledge that is necessary for impact assessment or restoration practice.
Decision-making with respect to human impacts can be viewed as a three-step process. First, there is the identification of a real or perceived impact. Second is the quantification of impacts by environmental scientists (i.e. assessment) and, finally, there is interpretation and planning with regard to social and economic outcomes by managers and stakeholders.
Studies of environmental impact are generally concerned with the effects of disturbance or contamination over some defined scale, which is assessed by comparing the disturbed site with one or more reference sites unaffected by the specific intervention under investigation. Reference sites can be thought of as a random sample from a population of sites as in design-based approaches (Underwood Reference Underwood1992), or as a set of covariates correlated with the disturbed site as in model-based analyses (Stewart-Oaten & Bence Reference Stewart-Oaten and Bence2001). Irrespective of the approach used, reference sites are selected from the same geographical area as the disturbed site and are supposedly exposed to the same mean environmental conditions (for example climate, seasonality and history). In this context, the general quality of the environment has no role in the assessment of the impact. Independently of perceptions of good or bad background conditions, it is the relationship between descriptors of assemblages at disturbed and reference sites that provides the evidence from which to make inferences about ecological impacts. It is only in relative terms that the magnitude, direction and severity of ecological responses to human disturbances can be scrutinized scientifically. Reference to unobserved unquantified past conditions is unnecessary and irrelevant for the assessment of alterations owing to specific human interventions.
Once detected and quantified, ecological impacts are interpreted with respect to a complex array of social and economic considerations. It is only at this stage that attributes of the system threatened, such as richness of species/habitats or proportion of rare or endangered species/habitats must be taken into account to assess the relevance of the environmental alterations, which will obviously vary from one system to another. The interpretation of changes is, therefore, not absolute, but contingent on the type of habitat and organisms under threat. For example, alterations viewed as reasonably negligible in a degraded urban area could be interpreted as severe in a National Park. This does not, by any means, imply that the consequences of human perturbations are not negative and not worth minimizing when alternative options are available. Unplanned ecological changes should be, by default, considered as negative, ensuring that there is consideration of the intrinsic negative consequences of unpredicted changes in ecological structure or function caused by human activities. This approach would contribute to the conservation of what is left of relatively undamaged habitats, because it implies that a case for tolerating some impact is actually made and justified. The actual occurrence or consequences of impacts may, however, be judged to be irrelevant or unacceptable for some specific background environmental conditions or affected social and economic conditions.
For example, Brown and Sax (Reference Brown and Sax2004) argued that the current concern for biological invasions is only partially justified, because comparable, or of even greater magnitude, extinctions and migrations of species have occurred in the past without human intervention. As a consequence, determining whether a particular current change in some recipient environment as a result of biological invasions is harmful remains a subjective, rather than an objective scientific endeavour. It could vary from positive to negative according to the prevalent economic and social activities taking place in the area and to the ecological awareness of the individuals affected by any environmental changes (Brown & Sax Reference Brown and Sax2004).
The same principle should be embraced even when unpredicted increases in numbers of species are produced as side-effects of human perturbations. An increase in the number of species has no intrinsic positive value. Some habitats have fewer species or are less productive than others, but this does not imply that they are not worth conserving. Conservation biologists must carefully avoid the pitfall of always defining increases in numbers of species as positive changes (Angermeier Reference Angermeier1994). Any increase in numbers and types of species may put more pressure on the resources needed by the native species. For example, if we generally consider more species to be a good thing, we would endorse attempts to replace arid lands or deserts with forests. Other attributes of natural assemblages, such as composition, frequency of occurrence and relative abundances of species, must obviously be considered when assessing impacts owing to humans.
A very different situation is that where human interventions pursue a well-defined goal that has been established a priori, as in restoration or rehabilitation. In such cases, the decision-making process is reversed in comparison to the evaluation of impacts and knowledge of past reference conditions can be required to set realistic goals and expectations. In this case, planning the specific changes as a consequence of ecological, social or economic needs then precedes the work of those scientists who have responsibility to achieve the defined goals. Here, the predicted changes, including increases in species diversity, are obviously given an intrinsic positive value. The same careful consideration should nevertheless be given to the consequences of restoration as to issues arising from impacts. For example, is restoration of urban wetlands which results in increased numbers of arthropod vectors of human diseases inevitably desirable?
In conclusion, unplanned alterations to natural systems, when detected relative to reference background conditions, either pristine or degraded, should always be considered a priori to be negative. This is so whether or not they are identified as increases or decreases in ecological variables (including the number of species in an area). Whether or not to tolerate or manage an increase (or, for that matter, a decrease) requires demonstration that the outcome will be predicted to be positive in the light of economic or social criteria, as suggested by Brown and Sax (Reference Brown and Sax2004). Unless changes caused by human activities are properly evaluated to be positive, they should be minimized as a continuing priority to aid conservation. Within this context, knowledge of past natural conditions can be crucial for rehabilitation and restoration practice, but irrelevant for the interpretation of human impacts.